/*-
 *  * Copyright 2016 Skymind, Inc.
 *  *
 *  *    Licensed under the Apache License, Version 2.0 (the "License");
 *  *    you may not use this file except in compliance with the License.
 *  *    You may obtain a copy of the License at
 *  *
 *  *        http://www.apache.org/licenses/LICENSE-2.0
 *  *
 *  *    Unless required by applicable law or agreed to in writing, software
 *  *    distributed under the License is distributed on an "AS IS" BASIS,
 *  *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  *    See the License for the specific language governing permissions and
 *  *    limitations under the License.
 */

package org.datavec.api.records;

import java.io.UnsupportedEncodingException;

/**
 * A byte sequence that is used as a Java native type for buffer.
 * It is resizable and distinguishes between the count of the sequence and
 * the current capacity.
 *
 */
public class Buffer implements Comparable, Cloneable {
    /** Number of valid bytes in this.bytes. */
    private int count;
    /** Backing store for Buffer. */
    private byte[] bytes = null;

    /**
     * Create a zero-count sequence.
     */
    public Buffer() {
        this.count = 0;
    }

    /**
     * Create a Buffer using the byte array as the initial value.
     *
     * @param bytes This array becomes the backing storage for the object.
     */
    public Buffer(byte[] bytes) {
        this.bytes = bytes;
        this.count = (bytes == null) ? 0 : bytes.length;
    }

    /**
     * Create a Buffer using the byte range as the initial value.
     *
     * @param bytes Copy of this array becomes the backing storage for the object.
     * @param offset offset into byte array
     * @param length length of data
     */
    public Buffer(byte[] bytes, int offset, int length) {
        copy(bytes, offset, length);
    }


    /**
     * Use the specified bytes array as underlying sequence.
     *
     * @param bytes byte sequence
     */
    public void set(byte[] bytes) {
        this.count = (bytes == null) ? 0 : bytes.length;
        this.bytes = bytes;
    }

    /**
     * Copy the specified byte array to the Buffer. Replaces the current buffer.
     *
     * @param bytes byte array to be assigned
     * @param offset offset into byte array
     * @param length length of data
     */
    public final void copy(byte[] bytes, int offset, int length) {
        if (this.bytes == null || this.bytes.length < length) {
            this.bytes = new byte[length];
        }
        System.arraycopy(bytes, offset, this.bytes, 0, length);
        this.count = length;
    }

    /**
     * Get the data from the Buffer.
     *
     * @return The data is only valid between 0 and getCount() - 1.
     */
    public byte[] get() {
        if (bytes == null) {
            bytes = new byte[0];
        }
        return bytes;
    }

    /**
     * Get the current count of the buffer.
     */
    public int getCount() {
        return count;
    }

    /**
     * Get the capacity, which is the maximum count that could handled without
     * resizing the backing storage.
     *
     * @return The number of bytes
     */
    public int getCapacity() {
        return this.get().length;
    }

    /**
     * Change the capacity of the backing storage.
     * The data is preserved if newCapacity >= getCount().
     * @param newCapacity The new capacity in bytes.
     */
    public void setCapacity(int newCapacity) {
        if (newCapacity < 0) {
            throw new IllegalArgumentException("Invalid capacity argument " + newCapacity);
        }
        if (newCapacity == 0) {
            this.bytes = null;
            this.count = 0;
            return;
        }
        if (newCapacity != getCapacity()) {
            byte[] data = new byte[newCapacity];
            if (newCapacity < count) {
                count = newCapacity;
            }
            if (count != 0) {
                System.arraycopy(this.get(), 0, data, 0, count);
            }
            bytes = data;
        }
    }

    /**
     * Reset the buffer to 0 size
     */
    public void reset() {
        setCapacity(0);
    }

    /**
     * Change the capacity of the backing store to be the same as the current
     * count of buffer.
     */
    public void truncate() {
        setCapacity(count);
    }

    /**
     * Append specified bytes to the buffer.
     *
     * @param bytes byte array to be appended
     * @param offset offset into byte array
     * @param length length of data
    
     */
    public void append(byte[] bytes, int offset, int length) {
        setCapacity(count + length);
        System.arraycopy(bytes, offset, this.get(), count, length);
        count = count + length;
    }

    /**
     * Append specified bytes to the buffer
     *
     * @param bytes byte array to be appended
     */
    public void append(byte[] bytes) {
        append(bytes, 0, bytes.length);
    }

    // inherit javadoc
    public int hashCode() {
        int hash = 1;
        byte[] b = this.get();
        for (int i = 0; i < count; i++)
            hash = (31 * hash) + (int) b[i];
        return hash;
    }

    /**
     * Define the sort order of the Buffer.
     *
     * @param other The other buffer
     * @return Positive if this is bigger than other, 0 if they are equal, and
     *         negative if this is smaller than other.
     */
    public int compareTo(Object other) {
        Buffer right = ((Buffer) other);
        byte[] lb = this.get();
        byte[] rb = right.get();
        for (int i = 0; i < count && i < right.count; i++) {
            int a = (lb[i] & 0xff);
            int b = (rb[i] & 0xff);
            if (a != b) {
                return a - b;
            }
        }
        return count - right.count;
    }

    // inherit javadoc
    public boolean equals(Object other) {
        if (other instanceof Buffer && this != other) {
            return compareTo(other) == 0;
        }
        return (this == other);
    }

    // inheric javadoc
    public String toString() {
        StringBuilder sb = new StringBuilder(2 * count);
        for (int idx = 0; idx < count; idx++) {
            sb.append(Character.forDigit((bytes[idx] & 0xF0) >> 4, 16));
            sb.append(Character.forDigit(bytes[idx] & 0x0F, 16));
        }
        return sb.toString();
    }

    /**
     * Convert the byte buffer to a string an specific character encoding
     *
     * @param charsetName Valid Java Character Set Name
     */
    public String toString(String charsetName) throws UnsupportedEncodingException {
        return new String(this.get(), 0, this.getCount(), charsetName);
    }

    // inherit javadoc
    public Object clone() throws CloneNotSupportedException {
        Buffer result = (Buffer) super.clone();
        result.copy(this.get(), 0, this.getCount());
        return result;
    }
}
